1. Field of the Invention
The field of the invention is improvements to solar water heaters and in particular to construction of absorber panels and apparatus for controlling freeze damage.
2. Description of the Related Art
Solar water heaters, in the last couple of decades, have had considerable impact upon homeowners and business largely because of the rising costs of fossil fuels. Improvements in solar water heaters were forthcoming regularly and now, to a large extent, construction of the solar water heater absorber has become somewhat standardized in a large number of the manufactured water heaters. The various major elements of solar water heaters comprise the absorber, i.e., that portion of the heater which directly receives the sun's rays and transfers the received heat energy to water or other fluids running through connected pipes or risers; the collector, i.e., the structure encapsulating the absorber in an insulated box-like frame with a transparent top; and the water storage tank usually distant from the collector.
There are two basic types of solar water heaters, the open and closed loop systems. In the closed loop system, water or antifreeze or other liquid is continuously circulated between the absorber on the roof and a heat exchanger interiorly to a water storage tank in the house. The water to be heated for residential or commercial use is in contact with the heat exchanger or radiator to receive the energy which has been brought down from the absorber on the roof area by means of pipes in a continuously circulating manner. In an open loop system, water which is used by the household or business is circulated through the absorber and then mixed with cold water for distribution as a hot water source. It may or may not be temporarily stored in a storage tank. If so, the storage tank is in line with the home water supply.
Construction of the absorber as standardly practiced generally takes the form of firstly placing a series of parallel semi-circular grooves in a piece of flat sheet metal, such as sheet copper, and then placing individual cross-runs or risers of copper pipe into these semi-circular grooves. The pipes are physically soldered to the sheet metal. Generally the sheet metal is rectangular in shape, being 3 to 4 feet in height and 8 to 10 feet in length. Often there may be 6 to 8 or more risers on one panel or sheet of the metal. The panel, when installed, is aligned long-ways, i.e., one of the length sides resting upon the roof. The panel is set to face the sun, sloped at an angle to the horizon, and painted black to more efficiently absorb the sun's rays. The copper pipes are usually on the underside (away from the sun) of the absorber panel.
At each end of the absorber panel is a transversely situated elongated pipe manifold to which each of the risers attached to the solar panel are connected. The manifold is not soldered or attached to the absorber panel. The water flows into one manifold on one side of the solar panel and then is transferred to the manifold on the opposite side through the horizontal risers soldered to the backside of the absorber panel.
The solar absorber, including the two side manifolds, are contained in a collector box, usually heat insulated on the sides and bottom, having a glass or clear plastic top through which the sun's rays pass. In most cases, water is introduced into the bottom of one manifold on one side of the absorber and removed at the top side of the opposite manifold. In operation, cold water is passed through the side of the collector to the absorber manifold to flow in parallel paths through the cross pipes soldered to the solar panel to the opposite manifold, the hot water rising and taken out from the opposite manifold at the other side of the collector.
Another variation of the solar absorber is to connect adjacent risers at opposite sides of the absorber in a fashion such that the water circulates in a serpentine fashion across the panel, the cold water entering at the bottom side of the absorber panel and then exiting at the top most riser at the side of the absorber panel.
The biggest problems occur during winter nights when the outside temperature drops below freezing and causes the water inside the pipe to freeze and thereby rupture the copper risers. Generally, the rupture will occur in that portion of the copper pipe soldered within the half-round groove formed in the absorber panel rather than that portion of the copper risers which are immediately accessible. After the water in the cross pipe freezes and causes the pipe to rupture, the ice in the pipe begins to melt during the late morning hours and water begins to leak from the pipe, remembering, especially in cases of open loop systems, that the solar water heater is still in the water distribution system. The collector fills with water which in turn then runs down the roof of the building.
As can be readily seen, repairs of commonly manufactured solar heaters is difficult. Firstly, the leak location has to be ascertained, the exactness of which may not be easy, and secondly, it is virtually impossible to repair the pipe for most leaks proximate the soldered portion next to the panel. Consequently, the pipe must be removed from the panel. This operation in itself takes considerable time and is more costly than just replacing the whole panel with a new panel, which is usually the case. As a consequence, repair of solar absorbers is very expensive, regardless of what method is used.
Thus it becomes readily apparent that there are improvements, which if added to the solar absorber panel, would benefit the industry for the absorbers which utilize the serpentine type water circulation. Firstly, to construct apparatus which would allow for freezing of the pipes in an absorber panel and would tolerate the freeze without rupturing the risers attached to the underside of the panel. To accomplish this, means must be incorporated within the piping system to accommodate the expanded ice and water. These means include the placement of a special freeze expansion pipe communicating with each riser which provides means to rupture a test cap by the freezing expanding water and allow escape of the water and ice which would otherwise cause the rupture.
It is also readily apparent that in the event of a very deep and hard freeze where even the above preliminary means taken to minimize damage were overcome by the hardness of the freeze, if the solar absorber were so constructed that individual risers in which water froze and ruptured could be quickly and easily removed, and done inexpensively, great improvement in the repair of solar water heaters benefit the industry.
It is therefore obvious that there is need for apparatus incorporated into the construction of solar water heaters which provide ways to minimize freeze damage in solar water heaters and which, in the event of a hard freeze and substantial damage to the solar water heater, still minimizes the repairs of the solar water heater.